The need for high bit-rate data transmissions through optical fibers presents significant challenges to the fiber-optic telecommunications industry. High bit-rate systems are highly susceptible to optical fiber nonlinearities. One option to confront these changes is to transmit the data in the Differential-Phase Shift Keying (DPSK) modulation format. The DPSK modulation format can transmit both RZ and NRZ data formats. One benefit of using the DPSK modulation format over the more standard On-Of Keying (OOK) modulation format is that, when DPSK signals are detected using a balanced receiver, the OSNR sensitivity is improved by up to 3 dB. See, for example, A. H. Gnauck and P. J. Winzer, “Optical Phase-Shift-Keyed Transmission,” IEEE Journal of Lightwave Technology, vol. 23, pp. 115-30, 2005.
The DPSK modulation format has numerous advantages over the OOK modulation format. However, the DPSK modulation format is more complicated than the OOK format. In DPSK systems, the digital information is written in the optical phase of the signal and, therefore, the digital information cannot be detected by ordinary intensity detectors. Consequently, DPSK receivers typically include optical demodulators, which convert the phase modulated signal to an amplitude modulated signal. The resulting amplitude modulated signal can easily be detected by ordinary power detectors.